As disclosed in Matsui et al., Chemistry Letters, 1981, pp. 1719-1720, it is known that aromatic iodides can be trifluoromethylated by reacting them with a large excess of sodium trifluoroacetate in the presence of cuprous iodide and a dipolar aprotic solvent. Matsui et al. also show that some trifluoromethylation occurs when an aromatic bromide is employed in the reaction instead of an iodide but that the yield of product is quite low.
Copending application, Ser. No. 724,474 (Ramachandran et al.), filed April 18, 1985, now U.S. Pat. No. 4,590,010, teaches that the technique of Matsui et al. is applicable to the trifluoromethylation of 6-alkoxy-5-halo-1-cyanonaphthalenes and the corresponding naphthoate esters--compounds which, like the compounds of Matsui et al., give better yields of the desired products when the halo substituent is iodo. Ramachandran et al. indicate that other trifluoroacetate salts can be used in their process, but they disclose a preference for using sodium trifluoroacetate as the trifluoromethylating agent.
Copending application Ser. No. 808,304 (Lin et al.), filed Dec. 12, 1985, teaches that potassium trifluoroacetate is more selective that sodium trifluoroacetate, can be used in smaller amounts, and does not require as long a reaction time when it is used to trifluoromethylate an aromatic bromide or iodide. Moreover, in contrast to the known processes utilizing the sodium salt, trifluoromethylations using the potassium salt can permit the products to be obtained in high yields even when the starting materials are aromatic bromides.